Methionine Binding to Dirhodium(II) Tetraacetate.

Area of Science:

• Coordination chemistry
• Bioinorganic chemistry
• Materials science

Background:

• Dirhodium(II) tetraacetate is an antitumor agent.
• Methionine is an essential amino acid.
• Understanding ligand exchange reactions is crucial for developing metal-based therapeutics.

Purpose of the Study:

• To investigate the reaction between dirhodium(II) tetraacetate and methionine in aqueous solution.
• To characterize the resulting adducts and their structural features.
• To explore the coordination modes of methionine to rhodium centers.

Main Methods:

• UV-vis spectroscopy
• Electrospray ionization mass spectrometry (ESI-MS)
• Rh K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy
• X-ray crystallography
• Size exclusion chromatography

Main Results:

• Initially formed 1:1 and 1:2 adducts of dirhodium(II) tetraacetate and methionine at room temperature.
• Methionine thioether confirmed to bind axially to dirhodium(II) cage.
• Stepwise displacement of acetate ligands by methionine observed with excess methionine.
• Stable dirhodium(II) species with two methionine ligands and two acetate ligands formed upon heating.
• Crystal structure revealed tridentate coordination of methionine to Rh(II) with thioether in equatorial positions.
• Minor monomeric rhodium(III) complex with tridentate methionine coordination (trans-S, N, O) also identified.

Conclusions:

• Methionine can coordinate to dirhodium(II) centers, displacing acetate ligands.
• Both Rh(II) and Rh(III) can form stable complexes with methionine.
• The coordination mode of methionine depends on the rhodium oxidation state and reaction conditions.
• These findings contribute to understanding the reactivity of dirhodium compounds with biological ligands.